Nowadays, various metal complexes comprising metal species and ligands are used as catalysts for organic synthesis reactions. It is known that factors for expression of the performance and activity of such a catalyst include not only the metal species but also the ligand in the metal complex, in other words, it is known that an organic compound having a group (coordination group) having lone pair electrons capable of coordinating to the metal species plays an extremely important role. Of such ligands, an organic compound (tridentate ligand) having three coordination groups has such a characteristic that the tridentate ligand binds to a metal species in a facial or meridional fashion to form a metal complex having two chelate rings. Moreover, a “Hemilabile” tridentate ligand, which has electrically inequivalent coordination groups, is known to be capable of functioning also as a monodentate ligand or a bidentate ligand in a catalyst cycle in a catalytic reaction. For this reason, changing the structures and the combination of the three coordination groups in a tridentate ligand in various manners makes it possible to adjust the structure, the physical properties, the catalytic activities, and the like of the corresponding metal complex at will. Accordingly, tridentate ligands and metal complexes thereof occupy important positions in the fields of synthetic organic chemistry, complex chemistry, catalyst chemistry, and the like, and are still being actively researched and developed. Especially, metal complexes of tridentate ligands having an imino group as a coordination group in each molecule are known to exhibit high catalytic activities in, for example, hydrogenation reactions of carbonyl compounds, dehydrogenation reactions of alcohols, and the like, and also the hydrogen atom on the imino group is known to exert great influences on the expression of activities in these catalytic organic synthesis reactions. Known examples of such a tridentate ligand include N,N-bis(2-phosphinoethyl)amine and N,N-bis(2-thioethyl)amine, which are symmetrical, and it is reported that ruthenium complexes thereof function as excellent catalysts in hydrogenation reactions of esters (Patent Literature 1 and Non Patent Literature 1). Here, these tridentate ligands having an imino group can be synthesized easily by simultaneously introducing phosphino groups or thio groups serving as the coordination groups to N,N-bis(2-chloroethyl)amine serving as a substrate. However, because of the chemically equivalent two chloro groups on the substrate, it is extremely difficult to successively and selectively introduce different coordination groups, which are important from the viewpoint of “Hemilability,” although the same coordination groups can be introduced. Therefore, there has been no report so far on any example of synthesis of N-(2-phosphinoethyl)-N-(2-thioethyl)amine, which would be obtained if successive introduction of a phosphino group and a thio group is conducted successfully. On the other hand, 2-phosphinomethyl-6-thiomethylpyridine derivatives, which are asymmetric tridentate ligands each having a phosphino group and a thio group and also having a pyridyl group instead of an imino group, and ruthenium complexes thereof are already known (Non Patent Literature 2). However, since the nitrogen atom is contained not in an imino group but in the pyridine ring, such a ruthenium complex is easily dimerized under a basic condition, while forming ruthenium-carbon bonds. This dimer is an inactive species in catalytic reactions, and hence causes problems of narrow scope of the reaction and poor activity.